Air brake with collet locked push rod and air supply system

ABSTRACT

An air brake includes a service brake chamber which actuates a push rod. A collet brake chamber is partially defined by a collet brake diaphragm. A locking collet is mounted to the collet brake diaphragm and includes a bore through which the push rod passes. A collet brake spring biases the collet into a tapered collet hole to clamp the collet onto the push rod to prevent the movement of the push rod toward the brake off position. Application of pressure to the collet brake chamber overcomes the force of the collet brake spring and moves the collet away from the tapered collet hole to allow the push rod to move freely. An air supply system, including a quick release valve, a two way check valve, an emergency and parking air supply tank and a pilot check valve, in conjunction with a conventional quick release valve or another type of exhaust valve, automatically supplies air to the service brake chamber from the tank whenever the spring brake supply line is vented. The air supply system can also be used with conventional air brakes.

This application is a reissue of application Ser. No. 06/638,441 filedAug. 7, 1984, now U.S. Pat. No. 4,589,704 issued on May 20,1986..Iaddend.

BACKGROUND OF THE INVENTION

Trucks, as well as other larger vehicles, generally use air brakes forstopping for both the tractor and the trailer. Air brakes include aservice brake chamber which drives a push rod into a brake on positionwhen air is applied to the service brake chamber. For parking purposes,a dual chamber air brake is often used. These dual chambered brakesinclude both a service brake chamber, for applying the brakes duringnormal operation, and what is called a spring brake chamber. The springbrake chamber includes a relatively heavy spring connected to the pushrod. The spring is compressed only when air from a spring brake line isapplied to the spring brake chamber. When the air in the spring brakechamber is vented, the spring brake spring drives the push rod to abrake on position. Thus, when a truck is parked and the air in the brakechambers is vented, the service brake chamber no longer actuates thebrakes but the spring brake spring pushes the push rod into a springbrake on position thus applying the brakes.

Conventional dual chamber brakes can only be made so that the brakingforce applied by the spring brake spring is only about half of thebraking force applied by the pressurization of the service brakechamber. This has made the use of the legal parking brake inadequate foremergency braking requirements, and has limited its effective usage toparking brake requirements only. The rationale for this seeminglydefective design is that the spring brake chamber may be vented whilethe service brake chamber is pressurized; when this occurs the totalforce on the brake is greater than that of the service brake alone. Ifthe spring brake spring were made large enough to equal the forceresulting from the pressurization of the service brake chamber, theforce applied to the brakes would be about double that applied by theservice brakes alone. This excess loading may lead to cracked drums andother premature failure. Thus the spring brake force is necessarily andcommonly limited to about 50% of the service brake force. Recently thereare means available to prevent the compounding of the service andparking brakes forces. See U.S. Pat. No. 4,407,548.

At present, there are no statutes which provide for emergency brakes forair braked vehicles. There are statutes which govern parking brakes, andair braked vehicles must have them. The USA, Asia and Europe haveaccepted the spring brake for parking brake requirements only and havenot yet specified it for any emergency brake requirements. Sincesomething is better than nothing, the trucking industry uses their legalparking brake for emergency situations because nothing else exists forthem to use, if the service brakes fail when a vehicle is in motion.However, because of the limited stopping power of spring brakes, andsince they are usually not used on all braked wheels, they are noteffective replacements for the service brakes which are designed to stopa vehicle in motion.

The Bendix Corporation of Southfield, Michigan sells two models of airbrakes, identified as DD-3 and SD-3 safety actuators, with mechanicallylocked push rods. The Bendix safety actuators include a number ofrollers wedged by a spring between the push rod and an inclined collarramp. During normal running conditions, that is when the spring brakeline is pressurized, air pressure in the spring brake line pushes apiston against the rollers to move the rollers up the ramp so that therollers move away from the push rod. When the spring brake line isvented, such as when parked, the piston returns allowing the rollers,under the influence of the spring, to be wedged against the collar rampand the push rod; this locks the push rod in place.

When using the Bendix safety actuator, the brakes do not release bynormal means. That is, people in the trucking industry are used tohaving the parking brakes release when the air pressure comes up.However, with the Bendix safety actuators, one cannot always release theparking brake unless an application of the service brake is also made.Also, application of the Bendix safety actuators requires that thevehicle's service brakes bring the vehicle to a stop before theirapplication. Therefore, the Bendix safety actuators are usable only forparking, not emergency purposes, if a vehicle's service brake is unableto stop the vehicle while moving. The Bendix actuator is complex,requires many precision machined parts and needs perfect seals. It isthus quite expensive. At present the only equipment of which applicantis aware using the DD-3 and SD-3 are GMC transit buses. These drawbacksmay account for the limited acceptance the Bendix safety actuators haveachieved.

International Transquip Industries, Inc. of Houston, Texas sells an airactivated mechanically held brake under the trademark Mini-Max. Thebrake is used with a conventional relay emergency valve for emergencyapplication. For parking, serrations on the push rod are engaged by theserrated end of a piston to lock the push rod in place. This occurs whenair pressure in the emergency tank is lost. Because of the loads and theenvironment encountered during use, it is expected that the serratedmembers would need to be made of expensive metals to achieve long lifefor this combination service and parking brake.

SUMMARY OF THE INVENTION

The present invention provides a pressurized fluid actuated brake,particularly useful as an air brake for trucks, which is simple andrugged in construction. Another aspect of the invention provides an airsupply system for allowing the automatic activation of the servicebrakes in the event of loss of pressure in a vehicle's air supply line,such as if the trailer breaks loose from its tractor.

An air brake made according to the invention includes a service brakechamber and a collet brake chamber. When the service brake chamber ispressurized, a push rod is driven into a brake on position by thepressurized air. When the service brake chamber is vented, the push rodis biased to a brake off position by a return spring. The service brakechamber is partially defined by a service brake diaphragm having anouter surface against which an enlarged, flattened end of the push rodpresses.

The housing also includes a collet brake chamber partially defined by acollet brake diaphragm. A locking collet, having a bore through which aportion of the push rod passes, is mounted to the collet brakediaphragm. A collet brake spring biases the collet into a tapered collethole defined by the housing. This clamps the radially flexible colletfingers against the push rod to halt movement of the push rod toward thebrake off position. Application of pressure to the collet brake chamberovercomes the force of the collet brake spring and moves the collet awayfrom the tapered collet hole; this allows the push rod to move freely.The collet brake chamber replaces the spring brake chamber found onconventional dual chambered air brakes. The collet brake chamber ispressurized by what is somtimes called the spring brake supply line orthe air supply line in conventional air brake systems; this same linewill sometimes be called the collet brake supply line in thisapplication.

Another aspect of the invention relates to an emergency and parking airsupply system (E&P system). This aspect of the invention ensures that ifpressure is suddenly lost to the collect brake supply line, pressurizedair will automatically be applied to the service brake chambers toeffectively stop the vehicle even if pressure is also lost in theservice brake application line. This aspect of the invention is alsousable with conventional service brakes as well.

The E&P system includes an emergency and parking pressurized air storagetank (E&P tank) mounted within the vehicle to be protected, typically atractor or a trailer. A conventional quick release valve has its inletconnected to the collet brake supply line, its chamber port connected tothe E&P tank and its exhaust port connected to an inlet of a two waycheck valve (TWC valve) via a connecting conduit. Instead of a quickrelease valve other valves, such as a two way check valve modified toinclude a spring for normally biasing the sealing member (commonly aball) toward the inlet connected to the collet brake supply line, can beused. However, a quick release valve is preferably used in thisnon-standard manner since it is commercially available. The quickrelease valve and the pilot check valve can be combined into a singlevalve structure to simplify installation and lower the cost of thesystem. Initial pressurization of the collet brake supply line fills theE&P tank.

The outlet of the TWC valve is connected to the inlet port of an exhaustvalve. The exhaust valve is preferably a quick release valve, but mayalso be a relay valve or a relay emergency valve, all three beingcommercially available. The exhaust valve includes one or more chamberports, connected to one or more service brake chambers, and an exhaustport for venting air in the service brake chambers to atmosphere whenthe air pressure at its inlet port is released. However, the E&P systemcan be used without an exhaust valve by allowing the exhaust port of thevehicle's foot valve to vent exhaust air pressure from the vehicle'sservice brake chambers. It is slower, however. The other inlet of theTWC valve is connected to the service brake application line.

The connecting conduit, and thus the opposed inlet of the TWC valve andexhaust port of the quick release valve, are maintained at atmosphericpressure so long as the collet brake supply line is at an elevatedpressure. This permits the unimpeded flow of air pressure from thecollet brake supply line and service brake application line to the E&Ptank and the exhaust valve, respectively, during normal operation. Thisis preferably accomplished using a pilot check valve having a controlport connected to the collet brake supply line, an inlet opening to theambient atmosphere and an outlet connected to the connecting conduit.See U.S. Pat. No. 4,407,548. The pilot check valve can be replaced byother valves operating in a similar manner. For example, a pilot bleedervalve made by The Aro Corporation of Byron, Ohio as Model 9600, is muchsmaller and less expensive than a conventional pilot check valve and canbe used instead of the pilot check valve. Pressure at the control portpermits the free fluid flow between the pilot check valve inlet andoutlet while a reduced pressure at the control port blocks passage offluid from its inlet to its outlet.

Upon venting of the collet brake supply line, either by design or byaccident, high pressure air will be automatically supplied to theservice brake chambers via the exhaust valve from the service brakeapplication line, if that is pressurized, or the E&P tank if it is not.In either event full service brake braking force is applied to the pushrod to effectively stop the vehicle.

The primary advantage of the collet brake of the present invention isthat during emergency braking 100% of the service brake braking force isavailable for stopping the vehicle. This is quite an improvement overconventional spring brakes which apply only about 50% of the servicebrake braking force.

Another important advantage is that the braking force applied by thecollet is mechanical. That is, the collet brake spring applies amechanical locking force which locks the collet onto the push rod, thusmaintaining the brakes in position. Thus the present invention meets thecurrent U.S. Motor Carrier Safety Regulations for parking brake systems,because when parked, the collet brake spring and collet holds the brakein position using mechanical energy, as opposed to hydraulic, pneumatic,or electrical energy which are illegal for this purpose.

Another advantage of the present invention is that regardless of whetheror not the collet is locked on the push rod, the service brakes canalways be applied. The force on the push rod applied to the servicebrake chamber is sufficient to overcome the collet brake spring thusmoving the collet out of engagement with the collet hole; once thisoccurs, the push rod slides within the collet bore to move to the brakeapplied position.

A further advantage of the present invention arises out of thesimplistic and economical nature of the collet locking mechanism used tosecure the push rod in place. Once the collet is locked in place, theforce of the push rod tends to increase the wedging force applied to thecollet thus compounding the wedging force applied by the collet brakespring. Further, the collet is self-aligning within the tapered collethole to reduce problems caused by cocking of the push rod. Also, thecollet can engage a substantial surface area of the push rod so the pushrod can be locked within the collet at relatively low surface pressureson the push rod. This reduces surface deformation and wear and thereforepromotes smooth operation and long life.

To deactivate conventional spring brakes, the air pressure applied tothe spring brake chamber must be sufficient to overcome its heavy dutyspring. Thus, at present, it takes time for a tractor's air pressureproducing system to generate enough pressure to release the spring brakebefore a tractor or a trailer can be moved. With the present invention,however, the vehicle can be moved sooner than with conventional springbrakes because first, the collet brake locking spring is much weakerthan a conventional spring brake spring, and second, the collet needsonly to be moved a short distance to release the push rod, thus allowingthe push rod biasing spring to remove the brakes.

The cost of conventional spring brakes is so high that they are onlyrequired on one axle of a three axle tractor further reducing theavailable braking force during emergencies and while parked. An airbrake made according to the invention should be able to be manufacturedat about the same price or less than commercially available springbrakes. Therefore, a significant cost saving may be realized becausefewer units need to be used to obtain equal or greater performance whencompared with these conventional brakes. Also, an air brake madeaccording to the invention can be attached to the vehicle's servicebrake chamber and service brake supply lines in the same manner asconventional dual chambered service and spring brakes to reduceinstallation problems.

Most tractors and trailers have pressure tanks acting as the pressurizedair supply for their spring brakes. In such cases the spring brake airsupply tank can be used in lieu of a separate E&P tank; this is anespecially, attractive option when retrofitting a tractor's trailer'sair brake system with an E&P system of the invention.

A single E&P air supply system can be used to supply several sets of airbrakes if desired. One way to do so is to add a TWC valve between theservice brake line and each set of service brake chambers (2) one axleon each whee (1) inlet of each added TWC valve to the exhaust port ofthe E&P system's quick release valve. This would provide true emergencybrakes to the vehicle at low cost.

Many tractors have dual chambered air brakes on only 1 of 3 axles.However, there is often not room to replace the service brakes with dualchambered air brakes. In these cases, adding the E&P system of theinvention provides true emergency braking at each wheel at a reasonablecost, something not attainable with dual chambered air brakes.

Other features and advantages of the present invention will appear fromthe following description in which the preferred embodiments have beenset forth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of a first embodiment of an airbrake made according to the invention with the push rod in the brake offposition and the push rod free.

FIG. 2 shows the air brake of FIG. 1 but with the push rod in the brakeon position and the push rod locked in position.

FIG. 3 shows a second embodiment of the air brake of the invention inwhich the push rod is in the brake off position and the push rod isfree.

FIG. 4 shows the air brake of FIG. 3 with the push rod in the brake onposition and the push rod locked.

FIG. 5 is a simplified schematic representation of an air brake systemincorporating the emergency and parking air supply system of theinvention shown used with the air brake of FIG. 1 involving a one axletrailer.

FIG. 6 is a schematic representation of a second air brake system,incorporating the emergency and parking air supply system of FIG. 5, fora two axle air braked tractor using conventional service brakes at oneaxle and conventional dual chamber air brakes at the other axle.

.Iadd.FIG. 7 is a simplified schematic representation of an alternativeembodiment of the air brake system of FIG. 5 in which the exhaust valvehas been removed..Iaddend.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIGS. 1 and 2 an air brake 2 includes a housing 4 made upof first, second and third housing portions 6, 8 and 10 secured to oneanother by clamps 11. A service brake diaphragm 12 is mounted at itsperipheral edge 14 between housing portions 6 and 8 to define a servicebrake chamber 16 between the interior surface 18 of portion 6 and thediaphragm surface 20. A service brake line port 22 allows fluidcommunication between a service brake line, not shown, and service brakechamber 16.

A push rod 24 passes through an opening 26 in third housing portion 10.Push rod 24 has an enlarged outer end 28 positioned adjacent a surface30 of diaphragm 12 opposite diaphragm surface 20. Push rod 24 passesthrough a conical opening 31, defined by a conical surface 32, in abulkhead 34 of second housing portion 8. A return spring 36 is mountedbetween outer end 28 and bulkhead 34 to bias push rod 24 in thedirection of arrow 38, that is towards the brake off position of FIG. 1.Pressurization of service brake chamber 16 overcomes the relatively weakbiasing force of the return spring 36 to force push rod 24 in adirection opposite arrow 38 towards the brake on position of FIG. 2.

A collet brake diaphragm 40 is secured at its peripheral edge 42 betweensecond and third housing sections 8 and 10. A collet 44 is mounted to asurface 46 of diaphragm 40 by a number of screws 48 passing through acircular mounting flange 50 at one end of collet 44, diaphragm 40 andinto a mounting ring 52 positioned adjacent the opposite surface 54 ofdiaphragm 40. Diaphragm 40 supports collet 44 for limited axial movementparallel to push rod 24 and within conical opening 31.

Collet 44 also includes a number of resilient fingers 56 surrounding abore 58. The outer surface 60 of fingers 56 is tapered at an anglecomplementary with the taper of conical opening 32. A collet brakelocking spring 62 is mounted between the end 64 of third housing portion10 and mounting ring 52. Locking spring 62 normally biases collet 44 inthe direction of arrow 38 so that outer surface 60 is forced againstconical surface 32 thus forcing fingers 56 against push rod 24 lockingpush rod 24 in place. Push rod 24 is released by applying air pressureinto a collet brake chamber 66 defined generally between surface 46 ofdiaphragm 40 and an inner surface 68 of second housing portion 8.Pressurized air is introduced into chamber 66 through a collet brakeport 70 which is coupled to a collet brake supply line 144 as shown inFIG. 5. The collet brake supply line corresponds to the spring brakesupply line in conventional dual chamber air brake systems. Pressurizedair is prevented from escaping between outer surface 60 and conicalsurface 32 by a generally cylindrical seal 72. Seal 72 is secured tobulkhead 34 by screws 74 passing through a ring retainer 76 and anannular lip portion 77 of seal 72. Pressurizing chamber 66 causescylindrical portion 78 of seal 72 to press against collet 44 thussealing chamber 66 while allowing sufficient axial movement of collet44.

During normal driving, chamber 66 is pressurized so that push rod 24 isfree to move. This condition is shown in FIG. 1. Applying pressurizedair to port 22 drives push rod 24 in the direction opposite arrow 38 toa brake applying or brake on position. A bleed hole 79 vents a region 81behind diaphragm 12 to atmosphere. If it is desired to keep the brakesapplied, collet brake chamber 66 is vented through port 70 which allowslocking spring 62 to force collet 44 against conical surface 32. This isthe condition of FIG. 2. Once this occurs the pressure within servicebrake chamber 16 may be reduced. However, because of the frictionalengagement between push rod 24 and collet 44, attempted movement of pushrod 24 in the direction of arrow 38 tends to drive the collet furtherinto conical surface 32 thus increasing the frictional engagementbetween the collet and the push rod. This effectively locks the push rodin place to keep the brakes applied.

If, however, chamber 66 were vented while push rod 24 was in the brakeoff position of FIG. 1, collet 44 would tend to lock push rod 24 intoplace, that is in the brake off position. However, upon application ofpressure to port 22, service brake chamber 16 becomes pressurized. Theforce against diaphragm 12 is made to be substantially greater than theforce of locking spring 62 so that the application of this pressure toport 22 forces push rod 24 and collet 44 therewith towards the brakeapplied position, that is in the direction opposite arrow 38. Oncecollet 44 has moved slightly, the frictional force between the colletand the push rod is reduced sufficiently to allow push rod 24 to movetoward the brake on position while sliding through collet 44. Thus,regardless of the presence or absence of pressure applied to colletbrake chamber 66, the brakes can always be applied by pressurizingservice brake chamber 16.

Turning now to FIGS. 3 & 4, a second embodiment of the air brake of theinvention is shown. Air brake 80 includes a housing 82 comprising first,second and third housing portions 84, 86 and 88 secured to one anotherby clamps 89. A service brake diaphragm 90 is mounted between second andthird housing portions 86, 88 at its peripheral edge 92 to define aservice brake chamber 94 between a forward surface 96 of diaphragm 90and an opposed end surface 98 of second housing portion 86. Pressurizedair is introduced into chamber 94 through a service brake port 100. Port100 is connected to the vehicle's service brake application line,typically through an exhaust valve for more responsive operation.

A push rod 102 is mounted partially within third housing portion 88through an opening 104 in an end wall 106 of third portion 88. Push rod102 includes first and second portions 103, 105 secured to one anotheron either side of diaphragm 90 by screws 107. First portion 103 of pushrod 102, like push rod 24 of the embodiment of FIG. 1, has an enlargedend 108 which rests against a surface 110 of diaphragm 90. Secondportion 105 has an enlarged end 109 resting against surface 96 ofdiaphragm 90 and includes an elongate rod 99 which passes through a bore113 in portion 86. O-ring 101 are mounted within bore 113 contact rod 99to prevent air from leaking from chamber 94 through bore 113. A returnspring 112 biases push rod 102 in the direction of arrow 114, that istowards the brake of position of FIG. 3. Pressurization of chamber 94forces push rod 102 in the direction opposite arrow 114 to the brakeapplying or brake on position of FIG. 4.

A collet brake diaphragm 116 is mounted between first and second housingportions 84, 86 at its peripheral edge 118 to partially define a colletbrake chamber 115. As can be seen by reference to FIG. 1, air brake 80and air brake 2 both mount generally similar collets 44, 111 to theirrespective collet brake diaphragms 40, 116. The only difference is thata groove 121 is formed in the outer surface 60 of collet 111. Elementshaving the same reference numerals as the embodiment of FIG. 1, such asmounting ring 52 and locking spring 62, are the same and will not bedescribed again.

A seal 125 is mounted about collet 111 and includes an annular lipportion 126 and a cylindrical portion 127. The periphery of annular lipportion 126 is housed within an annular opening 117 in first housingportion 84 so the screws 74 of the embodiment of FIG. 1 are not needed.Also, sealing bead 119 extends inwardly from an end of cylindricalportion 78. Bead 119 fits within complementary groove 121 formed incollet 111. A bleed hole 130 is formed through second housing portion 86to vent a region 132 to atmosphere. Pressurization of collet brakechamber 115 presses annular portion 126 against housing portion 84 andcylindrical portion 127 against collet 111 thereby sealing chamber 115.This configuration, which eliminates the need for fasteners, aids theassembly of brake 80.

Outer surface 60 of collet 111 engages a conical surface 120 of aconical opening 122 formed in one end of first housing portion 84.Collet brake locking spring 62 biases collet 111 in the direction ofarrow 114 so that the outer surface 60 of fingers 56 press againstconical surface 120 to force the fingers against a second portion 105 ofpush rod 102.

Air brake 80 operates in a manner similar to air brake 2. Although theembodiment of FIGS. 3 and 4 appears to be somewhat more complicated thanthat of FIGS. 1 and 2, it has the advantage that the effective columnlength of push rod 102 is shorter than that of push rod 24, thusreducing any tendency for the push rod to buckle. However, buckling isminimized in the embodiment of FIG. 1 by the guidance provided by pushrod 24 passing through collet 44. Also, the physical size of air brake80 to the left of O-rings 101 can be made smaller than shown since theforce required to secure collet 111 is much less than that required todrive push rod 102. Doing so reduces the size, cost and weight of brake80. The lowered weight is important since it reduces the cantileverstresses on brake 80.

Referring now to FIG. 5, a further aspect of the invention, an emergencyand parking air supply system (E&P system) 136 is shown incorporatedinto an air brake system 138 for use on trailers. System 138 includes aconventional emergency and parking valve (E&P valve) 140 connected to afirst air pressure source 142, both on the tractor. During normaloperation E&P valve 140 allows pressurized air from source 142 to beprovided to a collet brake supply line 144. Line 144 is connected toport 70 of brake 2 so that during normal operation (such as when thevehicle is moving along a road) collet brake chamber 66 is pressurized.Actuating valve 140 allows the pressurized air within line 144 to bedumped to atmosphere through an exhaust port 146 in valve 140. Aconventional pedal valve 148 connects a second pressurized air source150 to a service brake application line 152 so that pressurized air fromsource 150 is supplied to line 152 when pedal valve 148 is actuated;pressurized air within line 152 is vented to atmosophere through anexhaust port 154 of valve 148 otherwise.

An emergency and parking pressurized air storage tank (E&P tank) 156 isfluidly connected to collet brake supply line 144 through a conventionalsingle chamber port quick release valve 158 by a conduit 160. Valve 158includes a chamber port 162 connected to E&P tank 156 and an inlet port164 connected to conduit 160. Valve 158 also includes exhaust port 166connected to a first inlet 172 of a TWC valve 168 by a connector conduit170. Valve 168 includes a second inlet 174 connected to line 152 and anoutlet 176 connected to an inlet port 178 of an exhaust valve 180.Exhaust valve 180 is, in the embodiment of FIG. 5, a conventional dualchamber port quick-release valve and includes chamber ports 182, 184 andan exhaust port 186. Valve 180 is constructed so that when pressure isapplied to inlet port 178, exhaust port 186 is sealed and pressurizedfluid is applied to chamber ports 182, 184. When pressure is removedfrom inlet port 178, chamber ports 182, 184 are fluidly connected toexhaust port 186 so that pressurized air within chamber conduits 188,190 which connect chamber ports 182, 184 with service brake chambers 16of air brakes 2, and thus the air within the service brake chambers, isdumped to atmosphere.

A pilot check valve 192 is mounted across valve 158. Pilot check valve192 includes a control port 194 fluidly coupled to conduit 160 by a line196 and an outlet 197 fluidly connected to connecting conduit 170 by aline 198. Valve 192 also includes an inlet 200 open to atmosphere. Valve192 is preferably of a type disclosed in U.S. Pat. No. 4,407,548 atFIGS. 2A or 2B. Valve 192 is configured to allow fluid to pass generallyunimpeded from inlet 200 to outlet 197 regardless of the pressure atcontrol port 194. However, upon application of a predetermined pressureto control port 194, fluid is allowed to pass from outlet 197 to inlet200 and thus be discharged to atmosphere.

During normal operation of the vehicle collet brake supply line 144 ispressurized sufficiently to apply a first pressure at control port 194sufficient to allow passage of fluid from outlet 197 to inlet 200;conduct 198 and connecting conduit 170 are thereby vented to atmosphere.When this occurs, air pressure within collet brake supply line 144 flowsthrough inlet port 164, through chamber port 162 and into E&P tank 156to fill it. Upon actuation of pedal valve 148, which pressurizesapplication line 152, pressurized air flows from second inlet 174,through outlet 176, through exhaust valve 180 and into service brakechambers 16 of air brakes 2. Both exhaust port 166 and first inlet 172are sealed because of the high pressure fluid applied to inlet port 164and second inlet 174. If collet brake supply line 144 is dumped toatmosphere, such as by actuating E&P valve 140 or by a catastrophicevent, such as having line 144 rupture, the pressure at control port 194drops sufficiently to seal outlet 197; at the same time exhaust port 166opens and inlet port 164 closes so connecting conduit 170 becomespressurized by the air from E&P tank 156. If service brake applicationline 152 is at a lower pressure than connecting conduit 170, TWC valve168 has its second inlet 174 sealed allowing air from E&P tank 152 topass through first inlet 172, outlet 176 and into inlet port 178 ofexhaust valve 180; pressurized air from E&P tank 156 is applied toservice brake chambers 16 through ports 22 to apply the brakes.

.Iadd.Referring now to FIG. 7, an E&P system 336 incorporated into anair brake system 338 similar to that of FIG. 5 is shown. The onlydifference is the removal of exhaust valve 180 so that the remainingelements retain the same reference numbers as the embodiment of FIG. 5.and lines 188, 190 are coupled at a junction 340. Therefore, when line152 is pressurized, the high pressure air passes through ports 174 and176 of TWC valve 168 and into lines 188, 190. When pedal valve 148 isreleased, it opens dumping air in line 152 through exhaust port 154.Exhausting air in line 152 permits air in lines 188, 190 to be exhaustedto atmosphere through TWC valve 168, line 152 and port 154. If line 144is pressurized, air from lines 188, 190 can also flow through lines 170,198 and out port 200 of pilot check valve 192. Thus, the embodiment ofFIG. 7 operates in substantially the same manner as the embodiment ofFIG. 5 with the exception that it takes a bit longer for the air inlines 188, 190 to exhaust to atmosphere..Iaddend.

Referring now to FIG. 6, an air brake system 202 is used with a pair ofconventional service brake chambers 204 on one axle and a pair ofconventional dual chamber air brakes 206 on the other axle. Dual chamberair brakes 206 each include a service brake chamber 208 and a springbrake chamber 210. Pressurized air is supplied to spring brake chambers210 from a pressurized air source 212 through a spring brake valve 214,a spring brake supply line 216, a conventional relay valve 218 and lines220 which connect a spring brake inlet 222 with chamber ports 224 ofrelay valve 218. Relay valve 218 is, as mentioned above, a type ofexhaust valve, and is used to speed up pressurizing and exhaustingspring brake chambers 210. To do so, valve 218 is connected to anauxiliary pressurized air supply tank 226. The operation of this valveis conventional and is discussed with reference to FIG. 3 of U.S. Pat.No. 4,407,548. When no relay valve 218 is used, tank 226 is notconnected to the relay valve 218 and ports 222 are supplied directly.

Service brake chambers 208 and service brakes 204 are suppliedpressurized air from a pressurized air source 228 through a pedal valve230, a service brake application line 232, TWC valves 234, 236 and quickrelease valves 238, 240. In some cases, quick release valves are notused. Lines 242, 244 connect chamber ports 246, 248 of quick releasevalves 238, 240 with the inlets 250, 252 of pilot check valves 254, 256.The outlets 258, 260 of valves 254, 256 are connected to chamber ports262, 264 of service brake chambers 208 and 204 respectively. The controlports 266 of pilot check valves 254 are connected to lines 220 by lines268 while control ports 270 of pilot check valves 256 are connected tospring brake supply line 216 by a common line 272.

The structure of FIG. 6 thus far described is quite similar to the airbrake system shown in FIG. 5 of U.S. Pat. No. 4,407,548 with theexception of the TWC valves 234, 236 and the use of relay valve 218 andtank 226. To ensure the emergency pressurization of service brakechambers 208 and 204, two separate emergency and parking air supplysystems (E&P systems) 274, 276 are incorporated into air brake system202. E&P system 274 includes a quick release valve 278 having an inletport 280 connected to spring brake supply line 216 by a line 282 and anexhaust port 284 connected to an inlet 286 of TWC valve 234 by line 288.A chamber port 290 of valve 278 is fluidly connected to tank 226 so thattank 226 acts as both a reservoir for the normal pressurization ofspring brake chambers 210 and also as an E&P tank for E&P system 274. Apilot check valve 292 is used for the same purpose as pilot check valve192 of FIG. 5 to ensure that line 288 is maintained at ambient pressurewhenever spring brake supply line 216, and thus lines 220, arepressurized. Pilot check valve 292 includes a control port 294 connectedto line 268, an inlet 296 connected to ambient atmosphere and an outlet298 connected to line 288.

Referring now to E&P system 276 an E&P tank 298 is fluidly connected tothe chamber port 300 of a quick release valve 302. Valve 302 includes aninlet port 304 fluidly connected to spring brake supply line 216 by aline 306 and an exhaust port 308 fluidly connected to an inlet 310 ofTWC valve 236 by a line 312. A pilot check valve 314, used to ensureline 312 is maintained at ambient pressure when line 216 is pressurized,has its control port 316 connected to common line 272, its inlet 318connected to ambient atmosphere and its outlet 320 connected to line312.

In use, air brake system 202 normally has line 216 pressurized so thatspring brake chambers 210 are pressurized thus permitting brakeactuation based on the presence or absence of pressure in service brakeapplication line 232 which is controlled by the actuation of pedal valve230. Assuming line 216 is pressurized, applying pressure to line 232causes pressurized air flow through TWC valves 234, 236, quick releasevalves 238, 240, lines 242, 244 and pilot check valves 254, 256. Sinceline 220 is pressurized, control ports 266, 270 are supplied withpressurized air sufficient to allow free flow of air between inlets 250,252, and outlets 258, 260 of pilot check valves 254, 256.

Upon venting spring brake supply line 216 to atmosphere, spring brakechambers 210 are exhausted to atmosphere through their inlets 222,through lines 220 and out the exhaust port 232 of relay valve 218. Itshould be noted that relay valve 218 does not exhaust the pressurizedair within tank 226 when this occurs. This permits spring brake chambers210 to apply braking force to their associated brakes, not shown,according to the action of their spring brake springs in a conventionalmanner. Simultaneously, inlet ports 280, 304 of quick release valves278, 302 are also dumped to atmosphere thus sealing tanks 226, 298 fromlines 282, 306 to allow the tanks to pressurize lines 288, 312respectively. Since line 216 has been dumped to atmosphere, controlports 294, 316 of pilot check valves 292, 314 are also at reducedpressure so that pilot check valves 292, 314 no longer allow air withinlines 288, 312 to be exhausted to atmosphere. The high pressure air fromtanks 226, 298 is then supplied to service brake chambers 208 and 204 inthe same manner as in the embodiment of FIG. 5.

It should be understood that the braking force applied by air brakes 206will result from both the pressurization of service brake chambers 208and the spring braking force of spring brakes 210; when existing springbrakes are used this compounding of braking force would need to beconsidered in designing such a system. This force compounding problem isnot present when the E&P systems of the invention are used withconventional single chamber service brakes but result when existingspring brakes are used. Therefore the E&P systems of the invention findtheir greatest utility when used with air brakes incorporating colletlocked push rods according to the invention since full braking force isachieved without the force compounding problem and mechanical energy isused to hold the brakes on if application is made when vehicle is parkedor moving.

Modification and variation can be made to the disclosed embodimentswithout departing from the subject of the invention as defined by thefollowing claims. For example, either or both of the tapered collet andcollet hole may have a variable rate of taper rather than the constantrate of taper shown.

I claim:
 1. A pressurized fluid actuated brake comprising:a brakehousing defining a service brake chamber and a collet brake chamber; apush rod mounted to the housing for movement between brake on and brakeoff positions; means, including a service brake diaphragm operablycoupled to the push rod and responsive to the presence of a pressurizedfluid within the service brake chamber, for driving the push rod towardsthe brake on position when the service brake chamber is at a firstpressurized state; and collet means, operably coupled to the push rodand responsive to the presence of a pressurized fluid within the colletbrake chamber, for selectively restricting movement of the push rodtowards the brake off position, said push rod restricting meansincluding:a collet having a bore, a radially deflectable portionsurrounding at least a portion of the bore, said radially deflectableportion including an external surface; said housing defining a colletbore having an internal surface sized and positioned for matingengagemet with said external surface, at least one of siad internal andexternal surfaces being tapered; a collet brake diaphragm partiallydefining the collet brake chamber; means for mounting the collet to thecollet brake diaphragm for movement of the collet in response to thepresence of pressurized fluid within the collet brake chamber so to biassaid collet away from said collet bore to disengage said external andinternal surfaces when the collet brake chamber is at a secondpressurized state; said push rod including a movement limiting barpartialy housed within said bore and sized for complementary slidingengagement within the collet bore; and spring means for driving thecollet into the collet bore when said collet brake chamber is in a thirdpressurized state to lock the movement limiting bar in place therebyrestricting movement of the push rod towards the brake off condition. 2.The brake of claim 1 wherein said first pressurized state is an elevatedpressurized state relative to ambient pressure.
 3. The brake of claim 1wherein said second pressurized state is an elevated pressurized staterelative to said third pressurized state.
 4. The brake of claim 1wherein said internal and external surfaces are both tapered.
 5. Thebrake of claim 4 wherein said tapered internal and external surfaceshave the same taper.
 6. The brake of claim 1 wherein said brake on andoff positions are respective extended and retracted positions of saidpush rod.
 7. The brake of claim 1 wherein said push rod driving meansincludes a service diaphragm partially defining said service brakechamber.
 8. The brake of claim 7 wherein said push rod has an inner endabutting said service diaphragm whereby when the service brake chamberis in the first pressurized state said service diaphragm deflects saidpush rod to the brake on position.
 9. The brake of claim 8 wherein saidinner end has an enlarged flattened portion abutting the servicediaphragm.
 10. The brake of claim 1 further comprising a push rodbiasing spring mounted within the housing and arranged and adapted tobias the push rod towards the brake off position.
 11. The brake of claim9 further comprising a push rod biasing spring mounted within thehousing between an internal housing surface and the enlarged flattenedportion of the push rod.
 12. The brake of claim 1 wherein said movementlimiting bar is an intermediate portion of said push rod.
 13. The brakeof claim 9 wherein said movement limiting bar is an intermediate portionof said push rod.
 14. The brake of claim 8 wherein said push rodincludes a first portion one one side of said service diaphragm and asecond portion on the other side of said service diaphragm, said firstand second portions secured to one another to capture said servicediaphragm therebetween.
 15. The brake of claim 1 wherein said colletbiasing means further comprises a collet brake diaphragm partiallydefining said collet brake chamber and means for mounting said collet tosaid collet brake diaphragm so said collet moves with said collet brakediaphragm.
 16. The brake of claim 15 wherein said collet driving springmeans includes a spring mounted on the side of the diaphragm oppositethe collet.
 17. A pressurized fluid actuated brake comprising:a housingdefining a service brake chamber and a collet brake chamber fluidlycoupled to respective service brake and collet brake ports; a push rodmounted to said housing for movement between brake on and brake offpositions; means for normally biasing said push rod toward the brake offposition; service brake diaphragm means, operably coupled to said pushrod and responsive to the fluid pressure within said service brakechamber, for driving the push rod towards the brake on position whenpressurized fluid is applied to the service brake chamber; said housingdefining a tapered collet hole bounded by an internal surface with afirst chosen taper; a locking collet having an internal bore sized forcomplementary sliding engagement over said push rod, a portion of thecollet having a tapered external surface within a second chosen taper,said portion including axially segmented portions; a collet brakediaphragm mounted to the housing and partially defining the collet brakechamber; means for mounting said collet to the collet brake diaphragmfor movement of the collet in response to the fluid pressure withn thecollet brake chamber so to drive the collet out of engagement with thecollet hole internal surface when pressurized fluid is applid to thecollet brake chamber; spring means for normally biasing said collet intoengagement with said tapered colet hole so the tapered external colletsurface and tapered collet hole internal surface are forced against oneanother to bias the collet segmented portions against the push rod tokeep the push rod from moving from the brake on to the brake offposition; and whereby the push rod is free to move between brake on andbrake off positions when pressurized fluid is applied to the colletbrake chamber and the push rod is locked in position when pressurizedfluid is removed from the collet brake chamber.
 18. A pressurized fluidactuated brake comprising:a housing defining a service brake chamber andan collet brake chamber fluidly coupled to respective service brake andcollet brake ports; a service brake diaphragm and a collet brakediaphragm mounted within said housing and partially defining saidservice brake and collet brake chambers respectively; a push rod mountedto said housing for movement between brake on and brake off positions,said push rod having a first portion housed within said housingconfigured for operable engagement with a first side of said servicebrake diaphragm, said service brake diaphragm arranged and adapted todrive the push rod first portion towards the brake on position whenpressurized fluid is applied to the service brake chamber; means fornormally biasing said push rod first portion toward the brake offposition; a second push rod portion, including an elongate rod portionand an end secured to said first push rod portion with said servicebrake diaphragm therebetween; said housing defining a tapered collethole bounded by an internal surface with a chosen taper; a lockingcollet mounted to said collet brake diaphragm, said collet and colletbrake diaphragm arranged and adapted to drive the collet of engagementwith the collet hole internal surface when pressurized fluid is appliedto the collet brake chamber, said collet having an internal bore sizedfor complementary sliding engagement over said elongate rod portion ofsaid control push rod portion, a portion of the collet having a taperedexternal surface with said chosen taper, said collet portion includingradially movable segments; and spring means for normally biasing saidcollet into engagement with said tapered collet hole so the taperedexternal collet surface and the tapered collet hole internal surface areforced against one another to bias the collet segments against theelongate rod portion to keep the elongate rod portion from moving fromthe brake on the brake off position; whereby the push rod is free tomove between brake on and brake off positions when pressurized fluid isapplied to the collet brake chamber and the push rod is locked inposition when pressurized fluid is removed from the collet brakechamber.
 19. An emergency and parking brake air supply system for usewith air brake systems of the type including a brake chamber operablycoupled to a brake to apply the brake when the brake chamber ispressurized, a service brake application line and a spring brake supplyline, the system comprising:a pressure storage tank; a quick releasevalve including an inlet port, an exhaust port and a chamber port, saidchamber port fluidly coupled to said tank and said inlet port fluidlyconnected to the spring brake supply line; a two way check valveincluding first and second inlets and an outlet, said first inletfluidly connected to said exhaust port by a connection conduit and saidsecond inlet fluidly connected to said service brake application line;.Iadd.and .Iaddend. .[.an exhaust valve including an exhaust valve inletport fluidly connected to said two way check valve outlet, an exhaustvalve chamber port fluidly connected to said brake chamber and anexhaust valve exhaust port fluidly connected to the ambient atmosphere;and.]. a valve including a valve control port fluidly connected to saidspring brake supply line, a valve outlet fluidly connected to saidconnection conduit and a valve inlet fluidly connected to the ambientatmosphere, said valve arranged and adapted to block fluid flow fromsaid valve outlet to said valve inlet only when pressurized fluid belowa first pressure is applied to said valve control port and to vent theconnection conduit to atmosphere when the pressure at said valve controlport is above a second pressure; whereby venting said inlet port andsaid second inlet causes pressurized air within said tank to flowthrough said quick release valve, through said connection conduit,through said two way check valve.[., through said exhaust valve.]. andto the brake chamber.
 20. The system of claim 19 wherein said valve is apilot check valve arranged and adapted to permit generally free flow offluid from said inlet to said outlet at all times.
 21. An air brakesystem of the type including service brake and spring brake air supplysources, service brake and spring brake control valves fluidlyconnecting the service brake and spring brake air supply sources to aservice brake application line and a spring brake supply line, a servicebrake including a service brake chamber operably coupled to a brake toapply the brake when the service brake chamber is pressurized, thesystem comprising:an air supply system operably coupling said servicebrake chamber to the service brake air supply line comprising:a pressurestorage tank; a quick release valve including an inlet port, an exhaustport and a chamber port, said chamber port fluidly coupled to said tankand said inlet port fluidly connected to the spring brake supply line;atwo way check valve including first and second inlets and an outlet,said first inlet fluidly connected to said exhaust port by a connectionconduit and said second inlet fluidly connected to said service brakeapplication line; .Iadd.and .Iaddend. .[.an exhaust valve including anexhaust valve inlet port fluidly connected to said chamber port, anexhaust valve chamber port fluidly connected to said service brakechamber and an exhaust valve exhaust port fluidly connected to theambient atmosphere; and.]. a valve including a valve control portfluidly connected to said inlet port, a valve outlet fluidly connectedto said connection conduit means and a valve inlet fluidly connected tothe ambient atmosphere, said valve arranged and adapted to block fluidflow from said valve outlet to said valve inlet only when pressurizedfluid below a first pressure is applied to said valve control port so tovent the connection conduit to atmosphere when the pressure at saidvalve control port is above a second pressure; whereby venting saidinlet port and said second inlet causes pressurized air within said tankto flow through said quick release valve, through said connectionconduit, through said two way check valve.[., through said exhaustvalve.]. and to the service brake chamber.
 22. The system of claim 21wherein said valve is a pilot check valve arranged and adapted to permitgenerally free flow of fluid from said inlet to said outlet at alltimes.
 23. The system of claim 21 wherein said air brake includes aspring brake chamber fluidly connected to the spring brake supply line.24. The system of claim 21 further comprising a collet air brakeincluding:a brake housing defining and a collet brake chamber, saidcollet brake chamber being fluidly connected to the spring brake supplyline; a push rod mounted to the housing for movement between brake onand brake off positions; means, operably coupled to the push rod andresponsive to the presence of a pressurized fluid within the servicebrake chamber, for driving the push rod towards the brake on positionwhen the service brake chamber is at a first pressurized state; andcollet means, operably coupled to the push rod and responsive to thepresence of a pressurized fluid within the collet brake chamber, forselectively restricting movement of the push rod towards the brake offposition, said push rod restricting means including: a collet having abore, a radially deflectable portion surrounding at least a portion ofthe bore, said radially deflectable portion including an externalsurface; said housing defining a colet bore having an internal surfacesized and positioned for mating engagement with said outer surface, atleast one of said internal and external surfaces being tapered; means,responsive to the presence of pressurized fluid within the collet brakechamber, for biasing said collet away from said collet bore to disengagesaid external and internal surfaces whe the collet brake chamber is at asecond pressurized state; said push rod including a movement limitingbar, partially housed within said bore and sized for complenentarysliding engagement within the collet bore; and spring means for drivingthe collet into the collet bore when said collet brake chamber is in athird pressurized state to lock the movement limiting bar in placethereby restricting movement of the push rod towards the brake offcondition. .Iadd.25. The system of claim 21 further comprising anexhaust valve including an exhaust valve inlet port fluidly connected tosaid chamber port, an exhaust valve chamber port fluidly connected tosaid service brake chamber and an exhaust valve exhaust port fluidlyconnected to the ambient atmosphere..Iaddend.